This invention relates to liquid fertilizers, and more particularly to a liquid fertilizer of high nutrient value containing above about 35% by weight of the essential nutrients, and preferably above about 40% by weight of such nutrients: nitrogen (N), phosphorus (expressed in terms of phosphoruspentoxide-P.sub.2 O.sub.5), and potassium (expressed in terms of potassium oxide-K.sub.2 O).
Heretofore, a completely liquid fertilizer, free of precipitates, of relatively high nutrient value and containing all essential nutrients (nitrogen, phosphorus, and potassium) has been difficult to produce. U.S. Pat. Nos. 2,770,538 and 2,869,996 to Vierling are representative and disclose the mixing together of potassium hydroxide and phosphoric acid with ammonia, and possibly urea to produce a fertilizer having the claimed nutrient value: 10% N, 20% P.sub.2 O.sub.5, and 10% K.sub.2 O. The Vierling processes involve use of the essentially unstable ammonia, either in gaseous form or aqueous ammonia solution. U.S. Patent to Vierling U.S. Pat. No. 2,869,998 is similar, involving the further component nitric acid; in this case, a relatively low nutrient value product (8% N, 8% P.sub.2 O.sub.5, and 8% K.sub.2 O) is produced. U.S. Pat. No. 3,183,073 to Preston discloses a high nutrient value liquid fertilizer produced by use of a superacid (highly concentrated phosphoric acid and sucrose), together with ammonia and potassium hydroxide. U.S. Pat. No. 3,711,269 to Curless discloses a process for manufacturing liquid fertilizer utilizing potassium phosphate, phosphoric acid, and ammonia. In this case, the separation of precipitated solids and ammonia is required. U.S. Pat. No. 3,347,656 to Potts et al discloses a liquid fertilizer produced from potassium chloride, phosphoric acid, and ammonia, containing all three essential nutrients ranging from 10% to 60% by weight of the total product. U.S. Pat. No. 3,024,099 to Martinson disclosed a liquid fertilizer utilizing a fluosilicate. U.S. Pat. No. 2,950,961 to Striplin et al discloses a liquid fertilizer produced from ammonia, superphosphoric acid, potash salts. Liquid fertilizers from superphosphoric acids are discussed in Tennessee Valley Authority, Division of Chemical Development, "Proceedings of the Liquid Fertilizer Conference," 11 June 1959, by M. M. Striplin, Jr. The "Encyclopedia of Chemical Technology," third edition, volume 10, published by John Wiley & Sons, pages 98 to 105, contains a discussion of liquid mixed fertilizers.
In none of the above references is there disclosed a high nutrient value liquid fertilizer containing between about 6% to 9% N, 24% to 30% P.sub.2 O.sub.5, and 5% to 9% K.sub.2 O, which is produced by the use of reasonably stable component materials which are admixed together, as in the present invention. The present invention involves the reaction of ammonium phosphate solution, preferably containing polyphosphate and orthophosphate components, with phosphoric acid and a potassium-containing compound, such as potassium hydroxide, to produce such a high nutrient value liquid fertilizer which is stable over a wide range of temperatures and in which salts in solution do not precipitate out.